Stories of actual events in the creation of new aircraft designs. Explanations of the reasoning behind the airplane configuration arrangement and the modifications required for a successful product.

Thursday, March 8, 2007

TFX/F111 Page 2

As you can see right from the beginning these two requirements would be hard to do with a single airplane configuration.

In addition the AF airplane basic weapon system required a missile or bomb to be carried in an internal bomb bay. The Navy weapon system was the Phoenixsystem that required six externalmissile launch positions. There was no way to carry the Phoenix missiles in the limitedspace of the internal bay.

Ok, the above requirements are not totallyimpossible for a single design to handle, but there is stilla lot more to consider.

The most difficult thing is the basic size of the aircraft. For the AF if the airplane grows a little, no problem we need a little longer runway. If it gets a little heavy, we increase tire size etc.

However the Navy airplane must operate off an aircraft carrier. Now the Navy said it must not exceed55,000 pounds gross weight, and 56feet in length with a span shorter thanx feet with the wings folded or in this case retracted.

I don’t mean to overlook the tremendous effort made by GD and Grumman in proposingan airplane that can fly at mach 1.2 on the deck for almost 200 miles, and still be able to loiter for a few hours at 30000 feet while protecting the fleet with phoenix missiles, but the Navy version (F111B) was simply too heavy.

When the fourth proposal was about to be submitted the fall of 1962 a huge argument developed at Fort Worth. Grumman weights engineers came up with a gross weight estimate for the B version of approximately 65,000 pounds.

As Irecall General Dynamics weights reviewed the data that night and announced in the morning that their estimate was close to 60,000 pounds.

Grumman management backed the Grumman engineers and said Grumman could not support the proposal submittal, and sent every body on the Grumman team home. (Grumman had a team of bout 20 engineers working there in Fort Worth as part of the proposal effort)

Now I don’t want to suggest GD was fudging the numbers, but let us remember the final gross weight of the actual F111b was about 78,000 pounds.

I wasn’t back at Bethpage (the Grumman facility) for more than one day when I was called by the chief engineers secretary and told to get back to Fort Worth immediately. What happened was Grumman management agreed to keeping our name on the proposal , but words were added showing our reservation as regards the B model gross weight.

The Proposal Effort

There were many interesting events during the proposal efforts worth discussing that provide insight of how this airplane evolved.

First, there were two separate groups of engineers: the Texans and the Yankees ( actually the NY Yankees) One group dedicated to the Air Force and the other to the Navy.

However that was never a problem as we worked together very well.

The real problem was getting an overall configuration to contain all the equipment able to do the job and still fit on an aircraft carrier.

Let me explain. The most critical requirement was imposed by the AF need for the Mach1.2 200 mile dash on the deck. As I recall there were no airplanes or very fewflyingthat had ever exceeded Mach 1.0 at sea level. The TFX would do it at Mach 1.2 and for 200 miles!

So it was obvious this design had to have minimum frontal area. However the AF also required the airplane to be able to land on relatively soft terrain. I believe it had to be as soft as a UCI (Unit Construction Index)of around 5. Now don’t ask me why the AF needed to operate on such soft ground.

The Navy on the other hand was dealing with a steel carrier deck and could use extremely high tire pressure.

So the AF airplane gets huge tires and that kind of establishes just how big the body is going to be. Oh, I forgot the airplane is also a variable sweep wing design. The landing gear has to be stowed in the body. Add to the above the need for weapons storage, room for the large Phoenix system radar, and a side by side seated crew system, and you begin to see the design challenges.

(By the way, the only non-experimental variable sweep wing design ever built prior to the TFX was the Grumman F10F-1 Jaguar.( First flight May 19,1953) Unfortunately the 10F was ,to say the least, not a very good airplane. But the mechanics of the sweeping wings and the body mounted landing gear were excellent. That was the first airplane I worked on when I started at Grumman in 1950)